1. Field of the Invention
This invention relates to a method for correcting count rate losses of radiation events measured by a radiation detector, such as for example, a scintillation gamma camera, due to detector deadtimes during an acquisition time.
2. Description of Prior Art
Radiation detectors, such as for example, scintillation gamma cameras of the Anger type have data losses at high counting rates (see for example the essays "Deadtime Characteristics of Anger Cameras", by James A. Sorenson, Journal of Nuclear Medicine, April 1975, Vol. 16, No. 4, lines 284-288; and "The Influence of True Counting Rate and the Photopeak Fraction of Detected Events on Anger Camera Deadtime", by John E. Arnold et al., Journal of Nuclear Medicine, June 1974, Vol. 15, No. 6, lines 412-416). The correlation between counting losses and image distortion (i.e. attenuation) is for example described in the essay "Theoretical Studies of Image Artifacts and Counting Losses for Different Photon Fluence Rates and Pulse-Height Distributions in Single-Crystal Nal(T1) Scintillation Cameras" by Sren-Erik Strand et al., The Journal of Nuclear Medicine 1980, Vol. 21, pages 264-275.
Some correction for the events lost due to dead time (including pile-ups) has been tried by introducing a multiplication factor to scale the data that is detected after it has been received (an "after the fact" correction) as described for example in the essay "Correction for Deadtime Losses in a Gamma Camera/Data Analysis System", by K. Cranley et al., European Journal of Nuclear Medicine 5, 1980, Pages 377-382, in the U.S. Pat. No. 4,058,728 (Nickles) or U.S. Pat. No. 4,369,495 (Inbar et al.). To be accurate it would be necessary to know the relationship between the activity level and the event loss probability. The disadvantages of this technique are: that within each incremented time frame the dead time can change; the frame needs to be retained long enough to make the correction; and the relationship needs to be known between activity level and dead time.
Other correction for events lost has been tried by increasing the acquisition time in accordance with the level of activity to account for lost pulses as described for example in the essay "On The Performance of Loss-Free Counting-A Method for Real-Time Compensation of Dead-Time and Pile-Up Losses in Nuclear Pulse Spectroscopy", by G. P. Westphal, Nuclear Instruments and Methods 163 (1979) pages 189-196, North-Holland Publishing Co. This has a disadvantage for real time studies, such as cardiac flow, where comparisons are needed with equal time intervals.